Characterisation and determination of fullerenes: A critical review

A prominent sector of nanotechnology is occupied by a class of carbon-based nanoparticles known as fullerenes. Fullerene particle size and shape impact in how easily these particles are transported into and throughout the environment and living tissues. Currently, there is a lack of adequate methodology for their size and shape characterisation, identification and quantitative detection in environmental and biological samples. The most commonly used methods for their size measurements (aggregation, size distribution, shape, etc.), the effect of sampling and sample treatment on these characteristics and the analytical methods proposed for their determination in complex matrices are discussed in this review. For the characterisation and analysis of fullerenes in real samples, different analytical techniques including microscopy, spectroscopy, flow field-flow fractionation, electrophoresis, light scattering, liquid chromatography and mass spectrometry have been reported. The existing limitations and knowledge gaps in the use of these techniques are discussed and the necessity to hyphenate complementary ones for the accurate characterisation, identification and quantitation of these nanoparticles is highlighted.     

Current use of pressurised liquid extraction and subcritical water extraction in environmental analysis

This review updates our knowledge about pressurised liquid extraction (PLE) and subcritical water extraction (SWE), two sample preparation techniques which are increasingly used for the extraction of moderately and non-volatile organic pollutants from a variety of solid and semi-solid environmental matrices. Parameters influencing the extraction yield and selectivity are discussed. The results deriving from the analysis of several different classes of compounds in a variety of matrices are compared with a reference method, e.g., Soxhlet extraction. PLE and SWE are both promising techniques due to the short extraction times and low solvent consumption. In addition, SWE offers a wide range of polarities by changing the temperature and can easily provide class-selective extraction by temperature programming and/or the addition of modifier(s). This indicates that, even though many applications have already been reported, more can be expected.     

Sample treatment and determination of pesticide residues in fatty vegetable matrices: A review

A demanding task in pesticide residue analysis is yet the development of multi-residue methods for the determination of pesticides in vegetables with relatively high fat content (i.e. edible oils and fatty vegetables). The separation of pesticides and other chemical contaminants from high-fat food samples prior to subsequent steps in the analytical process is yet a challenging issue to which much effort in method development has being applied. This review addresses the main sample treatment methodologies for pesticide residue analysis in fatty vegetable matrices. Even with the advent of advanced hyphenated techniques based on mass spectrometry these complex fatty matrices usually require extensive sample extraction and purification. Current methods involve the use of one or the combination of some of the following techniques for both the sample extraction and clean-up steps: liquid-liquid partitioning, solid-phase extraction (SPE), gel-permeation chromatography (GPC), matrix solid-phase dispersion (MSPD), etc. An overview of methods developed for these contaminants in fatty vegetables matrices is presented. Sample extraction and purification techniques are discussed and their most recent applications are highlighted. This review emphasizes that sample preparation is a critical step, but also the determination method is, and cannot be treated separately from sample treatment. In recent years, the appearance and use of new, more polar pesticides has fostered the development of liquid chromatography/mass spectrometry (LC-MS) besides gas chromatography. The main features of LC-MS for the analysis of multi-class pesticides in fatty vegetable samples will be also underlined, with an emphasis on the multi-class, multi-residue strategy and the difficulties associated.     

Carbon‐based sorbents in chromatography. New achievements

The newest results in the employment of carbon‐based composites in various chromatographic techniques such as gas–liquid chromatography, high‐performance liquid chromatography and electrically driven separation techniques for the separation, quantitative determination and identification of a wide variety of compounds in complicated matrices are compiled. The results are concisely described and critically evaluated. The future trends in the application of carbon‐based compounds in the chromatographic separation methods are briefly discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of solvent and matrix combinations on the analysis of bacteria by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

The ability to rapidly identify the taxonomic class of the wide variety of microorganisms involved in human and animal disease is becoming increasingly important, especially with the increasing development of resistance to the antibiotics which form the main defence against them. A number of groups have recognised the utility of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry MALDI-TOF in the analysis of these microorganisms. However, no consistent methodology has been developed which is in general use. In particular the use of different solvent extraction systems and mass spectrometric matrices can have significant effects on the quality of the data obtained. We have now studied a number of the commonly used matrices and a range of solvent systems of widely varying polarity in an attempt to devise an optimum analytical strategy for the rapid characterisation of these organisms by MALDI-TOFMS. The E. coli ATCC 9637 organisms were initially washed to remove growth medium contaminants, followed by extraction with one of a range of solvents prior to admixing with a number of different single matrices or binary and ternary combinations of these matrices. The results obtained indicate that a binary combination of 2-(4-hydroxyphenylazo)benzoic acid and 2-mercaptobenzothiazole (1:1) as matrix provides the best data after the proteinaceous material from the organism cell surface was extracted with 17% formic acid, 33% isopropyl alcohol and 50% water, (solvent 2 in this work).     

On‐line solid‐phase extraction for liquid chromatography–mass spectrometry analysis of pesticides

Public concern about pesticides in food and water has increased dramatically in the last two decades. In order to guarantee consumers’ health and safety, analytical methods that could provide fast and reliable answers without compromising accuracy and precision are required. Sample treatment is probably the most tedious and time‐consuming step in many analytical procedures and, despite the significant advances in chromatographic separations and mass spectrometry techniques, sample treatment is still one of the most important parts of the analytical process for achieving good analytical results. Therefore, over the last years, considerable efforts have been made to simplify the stage and to develop fast, accurate, and robust methods that allow the determination of a wide range of pesticides without compromising the integrity of the extraction process. This review article intends to give a short overview of recently developed on‐line solid‐phase extraction, preconcentration, and clean‐up procedures for the determination of pesticides in complex matrices by liquid chromatography–mass spectrometry techniques.     

Review of the QuEChERS method for the analysis of organic pollutants: Persistent organic pollutants,polycyclic aromatic hydrocarbons,and pharmaceuticals

In multi-residue pesticide analysis, the quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction method has replaced less efficient traditional extraction methods due to its many advantages. In addition to pesticide analysis, this method has been widely used for the detection and analysis of pharmaceuticals, polycyclic aromatic hydrocarbons (PAHs), and several persistent organic pollutants (POPs), including dioxins, polychlorinated biphenyls, perfluoroalkyl substances, and brominated flame retardants in food, biological, and environmental matrices. The analysis of PAHs and POPs is challenging due to the properties of the target compounds and their low concentrations in complex matrices. This review summarizes previously reported the QuEChERS extraction approaches to the analysis of a wide range of analytes. The QuEChERS approaches, which include dispersive solid phase extraction (d-SPE), have generally been combined with either gas chromatography–mass spectrometry (GC–MS) or liquid chromatography–mass spectrometry (LC–MS) analysis. Further on, in recent years, GC and LC-tandem mass spectrometry has been utilized with the QuEChERS extraction due to its high selectivity, sensitivity, and specificity. This enables the extraction methods for target analytes to be modified through the selection of different extraction solvents, salt formulations, and buffers for salting-out partitioning and the selection of different d-SPE and SPE sorbents for the clean-up process. The most significant advantage of this method is that concentration steps are not required. This review aims to provide an up-to-date overview of information regarding the modification of extraction techniques based on target compounds and sample matrices.     

Isolation,Separation, and Preconcentration of Biologically Active Compounds from Plant Matrices by Extraction Techniques

Development of efficient methods for isolation and separation of biologically active compounds remains an important challenge for researchers. Designing systems such as organomineral composite materials that allow extraction of a wide range of biologically active compounds, acting as broad-utility solid-phase extraction agents, remains an important and necessary task. Selective sorbents can be easily used for highly selective and reliable extraction of specific components present in complex matrices. Herein, state-of-the-art approaches for selective isolation, preconcentration, and separation of biologically active compounds from a range of matrices are discussed. Primary focus is given to novel extraction methods for some biologically active compounds including cyclic polyols, flavonoids, and oligosaccharides from plants. In addition, application of silica-, carbon-, and polymer-based solid-phase extraction adsorbents and membrane extraction for selective separation of these compounds is discussed. Potential separation process interactions are recommended; their understanding is of utmost importance for the creation of optimal conditions to extract biologically active compounds including those with estrogenic properties.     

Evaluation of different sample treatments for determining pesticide residues in fat vegetable matrices like avocado by low-pressure gas chromatography-tandem mass spectrometry

A multi-residue method has been developed for determining 65 pesticide residues in greasy vegetable matrices such as avocado. Conventional organic solvent extraction assisted by a high-speed homogenizer was compared to pressurized liquid extraction (PLE) as extraction techniques. Following this, the lipophilic extract was purified using gel permeation chromatography (GPC). Alternative clean-up methods were also evaluated, as solid-phase extraction cartridges individually used and downstream coupled, but less effective lipophilic separation was archived. The pesticide residue determination was carried out using low-pressure gas chromatography coupled to tandem mass spectrometry (LP-GC-MS-MS), showing the applicability of this type of GC columns for the analysis of fat vegetable matrices. The proposed methodology was validated in avocado matrix. The recoveries were in the range 70-110%, with RSD values lower than 19%, at 12 and 50 microg/kg spiking levels. The limits of quantitation (LOQs) were in the range 0.04-8.33 microg/kg and the limits of detection (LODs) were between 0.01 and 2.50 microg/kg. All of them were lower than the maximum residue levels (MRLs) set by the European Union (EU) in avocado. The proposed method was evaluated analyzing pesticide residues in real avocado samples.     

Sample preparation for gas chromatographic determination of halogenated volatile organic compounds in environmental and biological samples

In this review, the wide spectrum of the techniques of isolation and/or preconcentration and final determination of halogenated volatile organic compounds (HVOCs) in water, air, soil, sediment and biological fluids are presented and discussed. The techniques discussed are solvent microextraction, solid phase extraction, gas extraction (static and dynamic techniques), membrane processes and passive sampling. Also, direct techniques, such as direct aqueous injection into gas chromatography (GC) column and membrane inlet mass spectrometry, are presented. Main attention is paid to the practical application of these techniques during all HVOCs determination.     

Coupling solid-phase microextraction to liquid chromatography. A review

Solid-phase microextraction (SPME) is a technique for extraction of organic compounds from gaseous, aqueous, and solid matrices. SPME is rapid and simple, ideal for automation and for in situ measurements, and no harmful solvents are needed. The principle of SPME involves equilibration of the analytes between the sample matrix and an organic polymeric phase coated on a fused-silica fiber. SPME is traditionally combined with analysis by gas chromatography (GC) and this combination has proved sensitive, accurate, and precise for quantitative analysis of different classes of volatile compound. More recently SPME has been coupled with liquid chromatography to widen its range of application to non-volatile and thermally unstable compounds also. This article reviews the status of SPME coupled with liquid chromatography. It focuses on different applications of the technique, e.g. environmental samples, biological fluids, and food samples, to show that SPME-HPLC has great potential in the analysis of a wide range of compounds in different matrices.     

Modern microextraction techniques for natural products

Natural product analysis has gained wide attention in recent years, especially for herbal medicines, which contain complex ingredients and play a significant clinical role in the therapy of numerous diseases. The constituents of natural products are usually found at low concentrations, and the matrices are complex. Thus, the extraction of target compounds from natural products before analysis by analytical instruments is very significant for human health and its wide application. The commonly used traditional extraction methods are time-consuming, using large amounts of sample and organic solvents, as well as expensive and inefficient. Recently, microextraction techniques have been used for natural product extraction to overcome the disadvantages of conventional extraction methods. In this paper, the successful applications of and recent developments in microextraction techniques including solvent-based and sorbent-based microextraction methods, in natural product analysis in recent years, especially in the last 5 years, are reviewed for the first time. Their features, advantages, disadvantages, and future development trends are also discussed.     

Novel contribution of chromatography in the development and analyses of metformin hydrochloride in biological and environmental samples

Globally, metformin hydrochloride (HCl) is the most commonly used antidiabetic drug and provides safe medication because of low risk of the side effects (lactic acidosis). Therefore, various researches have been established in pharmacodynamics and pharmacokinetic studies using various analytical applications such as calorimetry, spectrophotometry, and chromatography. But the chromatographic techniques are most widely used methods for the analysis of metformin HCl. This review discussed the different chromatographic methods used for the analysis of metformin HCl and its sample preparation for the isolation in different biological and environmental samples. Moreover, the mechanism for the fragmentation of ion products in LC–MS/MS is indicated for high throughput of the methods involved in the determination of metformin HCl in various sample matrices. The advancement in the chromatographic modalities provides the wide range of assays discussed herein.     

Extraction and clean-up strategies for the analysis of poly- and perfluoroalkyl substances in environmental and human matrices

The rapidly expanding field of per- and polyfluorinated alkyl substances (PFASs) research has resulted in a wide range of analytical methodologies to determine the human and environmental exposure to PFASs. This paper reviews the currently applied techniques for sample pre-treatment, extraction and clean-up for the analysis of ionic and non-ionic PFASs in human and environmental matrices. Solid phase extraction (SPE) is the method of choice for liquid samples (e.g. water, blood, serum, plasma), and may be automated in an on-line set-up for (large volume) sample enrichment and sample clean-up. Prior to SPE, sample pre-treatment (filtration or centrifugation for water or protein precipitation for blood) may be required. Liquid-liquid extraction can also be used for liquid samples (and does not require above mentioned sample pretreatment). Solid-liquid extraction is the commonly applied method for solid matrices (biota, sludge, soil, sediment), but automation options are limited due to contamination from polytetrafluorethylene tubings and parts applied in extraction equipment. Air is generally preconcentrated on XAD-resins sandwiched between polyurethane foam plugs. Clean-up of crude extracts is essential for destruction and removal of lipids and other co-extractives that may interfere in the instrumental determination. SPE, (fluorous) silica column chromatography, dispersive graphitized carbon and destructive methods such as sulphuric acid or KOH treatment can be applied for clean-up of extracts. Care should be taken to avoid contamination (e.g. from sample bottles, filters, equipment) and losses of PFASs (e.g. adsorption, volatilization) during sampling, extraction and clean-up. Storage at -20 degrees C is generally appropriate for conservation of samples.     

Phase analysis and reduction behaviour of Ce dopant in zirconolite

Accurate measurement of natural and anthropogenic radionuclide concentrations is of critical importance to end users in the nuclear sector to ensure correct classification prior to storage, recycling, reprocessing or disposal. Uncertainties in the characterisation of solid matrices and materials could lead to safety, quality and financial implications. Robust sample preparation methods are vital, in particular effective sample digestion, as under-estimated chemical yield recovery results in a corresponding under-estimation of activity levels. Borate fusion has been proven to effectively digest a range of complex sample matrices in the geosciences but is not used routinely elsewhere. In this study, we describe an automated procedure for borate fusion of multiple matrices encountered in nuclear decommissioning, containing diverse radionuclides over a range of activity concentrations. The impact of digestion flux, sample mass and sample to flux ratios are described, as well as the subsequent separation and measurement techniques. The results contribute to accurate and precise measurement of radionuclides in various matrices, as well as to characterisation of reference materials, providing greater confidence in nuclear industry programmes worldwide.

     

Developments in sample preparation and separation techniques for the determination of inorganic ions by ion chromatography and capillary electrophoresis.

A review is presented of sample preparation and separation techniques for the determination of inorganic ions by ion chromatography (IC) and capillary electrophoresis (CE). Emphasis has been placed on those sample treatment methods which are specific to inorganic analysis, and the developments in separation methods which are discussed are those which enhance the capabilities of IC and CE to handle complex sample matrices. Topics discussed include solid-phase extraction for sample clean-up and preconcentration, dialytic methods, combustion methods, matrix-elimination IC, electrostatic IC, electrically polarised ion-exchange resins, electromigration sample preparation in CE, chromatographic sample preparation for CE, use of high-ionic strength background electrolytes, buffering of background electrolytes in CE, use of capillary electrochromatography for inorganic determinations, and methods for the manipulation of separation selectivity in both IC and CE. Finally, some possible future trends are discussed.     

Recent advances of online coupling of sample preparation techniques with ultra high performance liquid chromatography and supercritical fluid chromatography

Ultra high performance liquid chromatography and supercritical fluid chromatography techniques are favored because of their high efficiency and fast analysis speed. Although many sample preparation techniques have been coupled with common liquid chromatography online, the online coupling of sample preparation with the two popular chromatography techniques have gained increasing attention owing to the increasing requirements of efficiency and sensitivity. In this review, we have discussed and summarized the recent advances of the online coupling of sample preparation with ultra high performance liquid chromatography and supercritical fluid chromatography techniques. The main sample preparation techniques that have been coupled with ultra high performance liquid chromatography online are solid‐phase extraction and in‐tube solid‐phase microextraction, while solid‐phase extraction and supercritical fluid extraction are the main techniques that have been coupled with supercritical fluid chromatography online. Especially, the strategies for online coupling of sample preparation with chromatography techniques were summarized. Typical applications and growing trends of the online coupling techniques were also discussed in detail. With the increasing demands of improving the efficiency, throughput, and analytical capability toward complex samples of the analysis methods, online coupling of sample preparation with chromatography techniques will acquire further development.     

Screening of pesticide-contaminated soil by supercritical fluid extraction (SFE) and high-performance thin-layer chromatography with automated multiple development (HPTLC/AMD)

A method for screening of pesticide-contaminated soil was developed. The extraction is carried out by supercritical carbon dioxide (CO(2)) with methanol as a modifier. The different components of the extracts are separated by high-performance thin-layer chromatography with automated multiple development (HPTLC/AMD) and evaluated densitometrically. The technique can be carried out without any previous clean-up step. Compared with other extraction techniques, SFE has the advantages of reducing the amount of co-extracted soil contents, which can seriously deteriorate the results. A 35-step development of the TLC-plate with gradient elution offers an application over a wide range of polarity. Migration data for 107 pesticides, recoveries and detection limits for 20 pesticides were determined.     

Rapid Methods in Analytical Chemistry

This article presents the most recent research in analytical chemistry concerning the development of rapid methodologies covering the period from 2009 up until today. In this context, different useful analytical methods have been developed based mainly on typical techniques such as gas chromatography, liquid chromatography, mass spectrometry, electrophoresis, electroanalytical chemistry, and biosensors. The analytical features of these methods have allowed the analysis of samples of different natures, such as environmental, food, pharmaceutical, and biological type, in which wide classes of analytes are promptly determined. The main advantages of these methods are included and discussed in this review regarding novelty, rapidity, sensitivity, selectivity, and costs. It is concluded that the development of rapid methods is still a growing trend in analytical chemistry and that gas- and liquid-chromatography mainly coupled to different modes of mass spectrometry are the most common analytical techniques applied today. Regarding the matrices analyzed, most of the methods have been developed for food analysis, followed by biological and environmental matrices.     

Rapid structural elucidation of composite bacterial hopanoids by atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry

Bacteriohopanepolyols (BHPs) are membrane lipids produced by a wide range of eubacteria. Their use, however, as molecular markers of bacterial populations and processes has until recently been hampered by the lack of a suitable rapid method for fingerprinting their composition in complex environmental matrices. New analytical procedures employing ion trap mass spectrometry now allow us to investigate the occurrence of BHPs in diverse biological and environmental samples including bacterial cultures, soils, and recent and ancient sediments. Here, we describe the structural characterisation using atmospheric pressure chemical ionisation liquid chromatography/ion trap mass spectrometry (APCI-LC/MS(n)) of a number of previously identified but less commonly occurring BHPs such as adenosylhopane and ribonylhopane. Many of the structures described here have previously only been reported in one or just a small number of cultured organisms having been isolated from large amounts of cellular mass (4-26 g) and identified by nuclear magnetic resonance (NMR) techniques after purification of individual compounds. Now, having established characteristic APCI fragmentation patterns, it is possible to rapidly screen many more bacterial cultures using only small amounts of material (<50 mg) as well as environmental samples for these atypical structures and a rapidly growing suite of novel structures.